Material Selection Guide

A material review starts by distinguishing conditions that must be satisfied from attributes that can be optimised. Mandatory items may include a customer specification, flame classification, food-contact declaration, disinfectant resistance, outdoor service life, minimum impact performance or a critical finished-wall dimension. Optimisation targets may include lower weight, shorter cycle time, a preferred gloss, easier painting or a cost objective. Treating every request as equally important produces an unfocused shortlist and makes trade-offs invisible.

We record each requirement with its source and verification method. “Outdoor use” is not enough: the review needs installation region, orientation, colour, expected life and acceptable appearance change. “High impact” is not enough: the likely impact energy, temperature, location and consequence of failure should be understood. Requirements that are still estimates are labelled as assumptions. This prevents an early quotation value from quietly becoming a production specification and gives the customer a clear list of decisions still to be confirmed.

Ditai can process heavy-gauge sheet from 1 to 12 mm, but starting thickness alone does not describe the strength of a thermoformed part. During forming, material moves into sidewalls, corners, flanges and deep features. Areas that travel furthest or stretch over a tight radius can become much thinner than the original sheet. Two parts made from the same 6 mm sheet may therefore have very different local walls and stiffness.

The engineering review identifies the zones that are likely to thin and compares them with functional requirements. Draw ratio, depth-to-opening relationship, sidewall angle, corner radius, feature spacing, plug assistance and sheet temperature distribution all influence material movement. A thicker sheet may help, but it can also increase heating time, forming load, trimming effort, weight and cost. The better solution may be a radius change, a shallower feature, local geometry support or a different forming strategy. For this reason, a thickness recommendation is expressed as a starting range until formed-wall measurements and part testing confirm it.

Customers often ask for the “strongest” plastic, but a housing normally fails through a specific mechanism: excessive deflection, local cracking, fastener pull-through, impact at a corner, creep under continuous load or distortion near heat. Stiffness and impact are not interchangeable. A stiff sheet can limit panel movement yet behave poorly under a sharp impact; a tough sheet can survive impact but still require ribs, returns or a supporting frame to control deflection.

We review span, mounting distance, load direction, edge support and whether the part is cosmetic, protective or structural. Large flat surfaces may need geometry that increases section stiffness rather than a simple increase in gauge. Fastener zones may require formed bosses, washers, inserts or load-spreading brackets. Where the enclosure has a safety role, representative impact and mounting tests are more meaningful than relying on a single datasheet value. Material, wall distribution and assembly design are evaluated as one system because changing any one of them can move the failure point.

The temperature question has several layers: normal operating temperature, short peaks, local heat sources, solar loading, transport and storage conditions, and the temperature applied during cleaning or downstream processing. A material with a suitable published heat value may still distort if a large panel is poorly supported or locked into an assembly that prevents thermal movement. Dark outdoor colours can experience substantially higher surface temperatures than the surrounding air, so ambient temperature alone is not a complete design input.

Cooling history also affects the finished geometry. Thick sections, uneven wall distribution and asymmetric trimming can create residual stress or warpage. The tool temperature, forming window, cooling time and demoulding condition must be repeatable. If tolerances are tight, the measurement method and conditioning time should be agreed before approval. Critical interfaces are best located and measured relative to stable datums rather than an uncontrolled cosmetic edge. The final decision may combine a higher-heat material with geometry, mounting clearance and process controls instead of expecting the polymer name to solve dimensional stability by itself.

Mould dimensions are developed for a defined material and process route. Different polymer families have different shrinkage behaviour, and even grades within a family can respond differently because of formulation, colour, sheet construction and processing history. Replacing ABS with PP, PE or another material after the tool is built is therefore not a simple purchasing substitution. The part may release differently, dimensions may move and trimming fixtures may no longer match.

At the start of a project we identify whether the tool is intended for one production material or must support a controlled alternative. Draft, undercuts, return geometry, texture, vacuum paths and plug design are reviewed together with the selected sheet. Prototype tooling can confirm general geometry, but a production approval should use the intended material construction and representative process settings. When a material change is requested later, the team reviews dimensional risk, surface reproduction, forming window and fixture compatibility before release. This protects the investment in moulds, CNC programs, assembly aids and inspection gauges.

Outdoor performance depends on more than adding a “UV” label. Resin grade, stabilisation package, colour pigment, cap layer, surface texture, sheet orientation and formed-wall distribution all contribute. An ABS/ASA construction can combine an economical ABS substrate with a weatherable ASA surface, but the cap must remain continuous and appropriate after the sheet stretches across the tool. Deep draws, sharp details and aggressive trimming can create areas that deserve additional review.

The project brief should define the installation climate, sunlight direction, temperature range, water exposure, pollutants, cleaning practice and target appearance life. Gloss retention, colour shift, chalking, cracking and loss of impact are different failure modes and may require different evidence. Accelerated weathering data can support comparison, but it does not reproduce every real climate or installation condition. For a demanding project, supplier data, a defined colour, retained samples and application-specific exposure or validation form a more defensible approval package than a broad promise of permanent UV resistance.

Chemical resistance tables are useful screening tools, but they rarely describe the complete finished-part condition. A cleaner may contact the surface as a brief wipe, repeated spray, trapped liquid around a fastener or long immersion. Concentration, temperature, dwell time and rinse procedure matter. Mechanical stress also matters: a plastic that tolerates a chemical as an unstressed coupon may craze or crack when the formed part is bent, fastened or carrying residual process stress.

We request the product name or chemical composition, concentration, contact frequency and application method. The review also considers oils, fuels, coolants, adhesives, paints, inks, disinfectants and release agents used during manufacturing or service. Transparent parts deserve particular attention because stress cracking and haze are immediately visible. When chemical exposure is important to safety, hygiene or service life, representative formed samples should be tested in the actual assembly condition. Passing a generic compatibility chart is not treated as proof for an unspecified cleaner and use cycle.

Appearance requirements affect both the sheet and the forming process. A colour target should reference a physical master, recognised colour system or approved sample, with an agreed tolerance and viewing condition. Screen images are not reliable colour standards. Gloss and texture can change visually after forming because the sheet stretches, the surface follows the tool and local wall thickness changes. Deep features may therefore appear different from broad shallow areas even when they come from one sheet.

We identify the customer-facing surface, allowable witness marks, protective-film requirement and whether the part will be painted, printed or used in moulded-in colour. Extruded texture can provide a consistent sheet surface and help disguise minor handling marks; tool texture follows different forming and tooling constraints. High-gloss and transparent surfaces require stricter sheet handling, clean tooling, careful trimming and protected packing. The drawing should mark Class-A zones and areas hidden after assembly so inspection effort is focused where appearance creates value.

A formed component is not finished when it leaves the mould. CNC trimming, drilling, routing, bonding, welding, painting, printing, hardware installation and assembly can expose weaknesses that were not visible during forming. A hole too close to a thinned corner can crack under tightening. A rigid adhesive joint can concentrate thermal stress. A paint or solvent system can attack the substrate. An unsupported flange can distort during machining.

The material recommendation therefore includes the intended secondary operations. Hole geometry, edge distance, screw type, washer, insert, torque and service access are reviewed for important mounting points. Bonded assemblies require compatible surface preparation and joint design, not only an adhesive name. Protective film and packing should remain compatible with the surface and removal conditions. Where tolerances depend on trim position, the locating scheme must reference stable formed features. Early review reduces late changes to fixtures, fasteners and assembly procedures and helps ensure that the chosen sheet remains suitable through the complete manufacturing route.

Terms such as flame-retardant, food-grade, medical-grade, antimicrobial or automotive-grade are not complete specifications. A claim may apply only to a named resin grade, colour, thickness, test method or supplier construction. The formed part can also introduce features, wall reductions, coatings or assemblies that are outside the scope of a sheet certificate. The customer should identify the governing standard, market, test level and documentation required for release.

Ditai can review candidate datasheets, declarations and certificates, but final compliance responsibility must be tied to the agreed production material and application. Material identity, supplier, colour, recycled content, cap construction and relevant batch records should be controlled when traceability matters. Substitutions require technical review rather than an assumption that two products with the same polymer abbreviation are equivalent. For regulated projects, samples and testing should represent the minimum relevant formed thickness and final construction wherever the applicable standard requires it.

Recycled material can support a sustainability target, but “recycled” does not describe one consistent engineering material. The source may be post-industrial or post-consumer, controlled or mixed, and the percentage may affect colour, odour, surface quality, forming behaviour and mechanical consistency. A visible housing, reusable tray and hidden liner will not need the same acceptance criteria. The project should define the recycled-content claim, traceability method and which performance requirements cannot be relaxed.

A co-extruded construction can sometimes place a controlled visible cap over a recycled substrate, helping balance appearance with recycled content. This still requires validation of adhesion, forming, cap continuity and performance. Colour range may be narrower, especially for light or highly controlled colours. We recommend approving representative samples and agreeing limits for visual variation before production. If the part has safety, food-contact, medical or tightly regulated duties, the available documentation and permitted material stream must be confirmed before recycled content is promised.

The final recommendation should state what has been confirmed and what remains to be demonstrated. A typical validation plan may include incoming sheet identification, thickness and colour checks, first-off forming trials, minimum-wall mapping, dimensional inspection, trim and assembly review, appearance approval and functional testing. Outdoor, impact, chemical, temperature or flame testing is added when the application requires it. Sample size, conditioning, acceptance limits and responsible party should be agreed rather than decided after a failure.

Production approval then links the accepted part to the sheet specification, mould revision, CNC program, process window and inspection method. Retained samples and controlled change records help investigate future variation. This approach avoids two common errors: treating a successful-looking prototype as proof of long-term performance, and treating a resin datasheet as proof of a finished thermoformed assembly. The objective is not unnecessary testing; it is a proportionate evidence chain that matches the consequence of failure and gives both customer and manufacturer a clear basis for release.